The present invention relates to a control system for controlling a production apparatus comprising a large number of devices, a production line comprising a number of such production apparatuses, and a production shop comprising a number of such production lines.
To be more specific, the present invention relates to a control system capable of executing a task instruction by performing distributed processing by means of a number of modules. The module which wants to have the task instruction done searches modules capable of executing it and allocates it to a selected module.
To control a cell (such as a production apparatus comprising a large number of structural elements) and a production shop (such as a production line having a group of production apparatuses), a control program is prepared and used. The control program is prepared on the basis of a configuration of the structural elements, the production apparatuses and the production line, and includes predetermined and fixed task allocations to the respective apparatuses.
If there is a change in the configuration, the entire control program has to be updated in accordance with such a change. For example, if one of the production apparatuses is changed to other one, the schedules have to be determined again with respect to all production apparatuses, including the existing ones.
The conventional control system described above does not comprise a means for flexibly coping with a change in the configuration of the apparatuses. This being so, the conventional control system has a poor adaptability with a production system of the next generation.
The production system of the next generation is required to satisfy the demand for prompt start of production and the demand for prompt and flexible response to a change in the amount of production or a change in the kind of items to be produced. In addition to these, there is a strong demand for more efficient use of production equipment. If the entire control program has to be reconstructed each time a product apparatus or a system is changed to satisfy the demands, the rate of productivity is inevitably very low.
Accordingly, an object of the present invention is to provide a control system capable of flexibly coping with a change in the configuration of a production apparatuses or the like.
To attain the object, the present invention provides a control system which executes task instructions and which comprises a higher-order module for making an inquiry as to whether or not a task instruction can be executed, and a lower-order module for determining whether or not the task instruction can be executed, in response to the inquiry made by the higher-order module, the higher-order module including a task instruction decomposition section for decomposing the task instruction into a sequence of task instructions executable by the lower-order module when the task instruction is inexecutable by the lower-order module, and a task instruction allocation section for allocating an executable task instruction to the lower-order module.
In the present invention, the higher-order and lower-order modules constitute a hierarchical structure, but the number of layers provided is not limited to these two. For example, it is possible to provide a higher-order module that is being treated as being higher than the higher-order module described above. Alternatively, it is possible to provide a lower-order module that is being treated as being lower than the lower-order module described above.
According to the control system of the present invention, the higher-order and lower-order modules are provided as unit modules, which are substantially the same in constitution and can be easily added, deleted or replaced. In preferred embodiments described below, the unit modules will be described as distributed and mutually-cooperative holon modules.
When a task instruction is input to the higher-order module described above, an inquiry is made to the lower-order module, and when necessary the task instruction is decomposed into instructions that are executable by the lower-order module. The higher-order module and the lower-order module do not have fixed relationships. In other words, their relationships are determined, depending upon the circumstances. In this manner, the hierarchical-structure system of the present invention is based on inquiries and responses. Irrespective of the structure of the lower-order module, the structure which can execute a sequence of task instructions can be reorganized. Hence, even where there is a change in the structure of the apparatuses, such a change can be flexibly coped with.
The modules described above can be realized as either hardware or software. They be can easily installed in a single apparatus; alternatively, they can be distributedly provided for apparatuses that are connected as a network.
According to the second aspect of the present invention, there is provided a control apparatus for controlling a system made up of a plurality of structural elements. The structural elements include a first means and a second means. The first means makes an inquiry to another structural element to check whether or not a designated instruction can be executed, and receives a response from that second structural element. Where there is a structural element that responds to the inquiry that the instruction is executable, the second means allocates the instruction to that structural element. If the second structural element makes the response that the task instruction is inexecutable, then the second means decomposes the task instruction. Then, the second means makes an inquiry once again to check whether or not the decomposed instructions are executable. The decomposition of instructions and the allocation of them are continued until the decomposed instructions can be executed.
With this constitution, the task instructions can be decomposed in such a manner that the structure which can execute the sequence of task instructions can be reorganized, irrespective of the structure of each structural element. It is therefore possible to expect the same advantages as attained in the first aspect of the invention.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.